DataSet and DataTable both implement IDisposable, so, by conventional best practices, I should call their Dispose() methods.

However, from what I've read so far, DataSet and DataTable don't actually have any unmanaged resources, so Dispose() doesn't actually do much.

Plus, I can't just use using(DataSet myDataSet...) because DataSet has a collection of DataTables.

So, to be safe, I'd need to iterate through myDataSet.Tables, dispose of each of the DataTables, then dispose of the DataSet.

So, is it worth the hassle to call Dispose() on all of my DataSets and DataTables?

Addendum:

For those of you who think that DataSet should be disposed:
In general, the pattern for disposing is to use using or try..finally, because you want to guarantee that Dispose() will be called.

However, this gets ugly real fast for a collection. For example, what do you do if one of the calls to Dispose() thrown an exception? Do you swallow it (which is "bad") so that you can continue on to dispose the next element?

Or, do you suggest that I just call myDataSet.Dispose(), and forget about disposing the DataTables in myDataSet.Tables?

I'd like to amend this answer and concede that the original answer was flawed.

The original analysis does apply to objects that require finalization – and the point that practices shouldn’t be accepted on the surface without an accurate, in-depth understanding still stands.

However, it turns out that DataSets, DataViews, DataTables suppress finalization in their constructors – this is why calling Dipose() on them explicitly does nothing.

Presumably, this happens because they don’t have unmanaged resources; so despite the fact that MarshalByValueComponent makes allowances for unmanaged resources, these particular implementations don’t have the need and can therefore forgo finalization.

(That .NET authors would take care to suppress finalization on the very types that normally occupy the most memory speaks to the importance of this practice in general for finalizable types.)

Notwithstanding, that these details are still under-documented since the inception of the .NET Framework (almost 8 years ago) is pretty surprising (that you’re essentially left to your own devices to sift though conflicting, ambiguous material to put the pieces together is frustrating at times but does provide a more complete understanding of the framework we rely on everyday).

After lots of reading, here’s my understanding:

If an object requires finalization, it could occupy memory longer than it needs to – here’s why: a) Any type that defines a destructor (or inherits from a type that defines a destructor) is considered finalizable; b) On allocation (before the constructor runs), a pointer is placed on the Finalization queue; c) A finalizable object normally requires 2 collections to be reclaimed (instead of the standard 1); d) Suppressing finalization doesn’t remove an object from the finalization queue (as reported by !FinalizeQueue in SOS)
This command is misleading; Knowing what objects are on the finalization queue (in and of itself) isn’t helpful; Knowing what objects are on the finalization queue and still require finalization would be helpful (is there a command for this?)

Suppressing finalization turns a bit off in the object's header indicating to the runtime that it doesn’t need to have its Finalizer invoked (doesn’t need to move the FReachable queue); It remains on the Finalization queue (and continues to be reported by !FinalizeQueue in SOS)

The DataTable, DataSet, DataView classes are all rooted at MarshalByValueComponent, a finalizable object that can (potentially) handle unmanaged resources

There are a lot of misleading and generally very poor answers on this - anyone who's landed here should ignore the noise and read the references below carefully.

Without a doubt, Dispose should be called on any Finalizable objects.

DataTables are Finalizable.

Calling Dispose significantly speeds up the reclaiming of memory.

MarshalByValueComponent calls GC.SuppressFinalize(this) in its Dispose() - skipping this means having to wait for dozens if not hundreds of Gen0 collections before memory is reclaimed:

With this basic understanding of finalization we
can already deduce some very important
things:

First, objects that need finalization
live longer than objects that do not.
In fact, they can live a lot longer.
For instance, suppose an object that
is in gen2 needs to be finalized.
Finalization will be scheduled but the
object is still in gen2, so it will
not be re-collected until the next
gen2 collection happens. That could be
a very long time indeed, and, in fact,
if things are going well it will be a
long time, because gen2 collections
are costly and thus we want them to
happen very infrequently. Older
objects needing finalization might
have to wait for dozens if not
hundreds of gen0 collections before
their space is reclaimed.

Second, objects that need finalization
cause collateral damage. Since the
internal object pointers must remain
valid, not only will the objects
directly needing finalization linger
in memory but everything the object
refers to, directly and indirectly,
will also remain in memory. If a huge
tree of objects was anchored by a
single object that required
finalization, then the entire tree
would linger, potentially for a long
time as we just discussed. It is
therefore important to use finalizers
sparingly and place them on objects
that have as few internal object
pointers as possible. In the tree
example I just gave, you can easily
avoid the problem by moving the
resources in need of finalization to a
separate object and keeping a
reference to that object in the root
of the tree. With that modest change
only the one object (hopefully a nice
small object) would linger and the
finalization cost is minimized.

Finally, objects needing finalization
create work for the finalizer thread.
If your finalization process is a
complex one, the one and only
finalizer thread will be spending a
lot of time performing those steps,
which can cause a backlog of work and
therefore cause more objects to linger
waiting for finalization. Therefore,
it is vitally important that
finalizers do as little work as
possible. Remember also that although
all object pointers remain valid
during finalization, it might be the
case that those pointers lead to
objects that have already been
finalized and might therefore be less
than useful. It is generally safest to
avoid following object pointers in
finalization code even though the
pointers are valid. A safe, short
finalization code path is the best.

Take it from someone who's seen 100s of MBs of non-referenced DataTables in Gen2: this is hugely important and completely missed by the answers on this thread.

Good point. How do you usually structure your code when you have a DataSet with many DataTables? Tons of nested using statements? A single try..finally to clean it all up at once?
–
mbeckishOct 21 '09 at 21:02

5

The statement "However, it turns out that DataSets, DataViews, DataTables suppress finalization in their constructors – this is why calling Dipose() on them explicitly does nothing." is a non-sequitur: the two concepts are largely unrelated; something that suppresses finalisation could still do something in Dispose(). Indeed , it actually makes more sense if we reverse it: Dispose() does nothing, which is why it suppresses finalisation in the constructor, i.e. because there would be nothing to do it doesn't want to bother the GC with calling the finaliser (which typically calls dispose).
–
Marc Gravell♦Aug 5 '12 at 11:43

Even if object has no unmanaged resources, disposing might help GC by breaking object graphs. In general, if object implements IDisposable then Dispose() should be called.

Whether Dispose() actually does something or not depends on given class. In case of DataSet, Dispose() implementation is inherited from MarshalByValueComponent. It removes itself from container and calls Disposed event. The source code is below (disassembled with .NET Reflector):

Indeed. I saw some code quite recently where lots of DataTables were created in a very large loop without being Disposed. This lead to all of the memory being consumed on the computer and the process crashing as it ran out of memory. After I told the developer to call dispose on the DataTable the problem went away.
–
RichardODMay 27 '09 at 17:56

You should assume it does something useful and call Dispose even if it does nothing in current . NET Framework incarnations, there's no guarantee it will stay that way in future versions leading to inefficient resource usage.

There's no guarantee that it will implement IDisposable in the future, either. I would agree with you if it were as simple as using(...), but in the case of DataSet, it seems like a lot of hassle for nothing.
–
mbeckishMay 27 '09 at 0:28

17

It fairly safe to assume that it will always implement IDisposable. Adding or removing the interface is a breaking change, whereas changing the implementation of Dispose is not.
–
Greg DeanMay 27 '09 at 0:35

4

Also, a different provider may have an implementation that actually does something with IDisposable.
–
Matt SpradleyMay 27 '09 at 13:22

Do you create the DataTables yourself? Because iterating through the children of any Object (as in DataSet.Tables) is usually not needed, as it's the job of the Parent to dispose all it's child members.

Generally, the rule is: If you created it and it implements IDisposable, Dispose it. If you did NOT create it, then do NOT dispose it, that's the job of the parent object. But each object may have special rules, check the Documentation.

For .net 3.5, it explicitly says "Dispose it when not using anymore", so that's what I would do.

From what I understand, the general consensus is that an object should dispose its own unmanaged resources. However, a collection of IDisposable objects will not in general iterate through its elements to dispose each one, because there might be other references to its elements outside of the collection: stackoverflow.com/questions/496722/…
–
mbeckishMay 27 '09 at 12:43

1

True, Collections are always something I consider special because they are usually not "doing" anything, they are merely... Containers, so I never bothered about that.
–
Michael StumMay 27 '09 at 14:24

If your intention or the context of this question is really garbage collection, then you can set the datasets and datatables to null explicitly or use the keyword using and let them go out of scope. Dispose does not do much as Tetraneutron said it earlier. GC will collect dataset objects that are no longer referenced and also those that are out of scope.

I really wish SO forced people down voting to actually write a comment before downvoting the answer.

I call dispose anytime an object implements IDisposeable. It's there for a reason.

DataSets can be huge memory hogs. The sooner they can be marked for clean up, the better.

update

It's been 5 years since I answered this question. I still agree with my answer. If there is a dispose method, it should be called when you are done with the object. The IDispose interface was implemented for a reason.

Calling dispose doesn't speed up the reclaiming of memory, to do that you would have to manually start the garbage collector which is generally a bad plan.
–
TetraneutronMay 26 '09 at 23:22

2

If Dispose sets a bunch of references to null, it can cause objects to be candidates for collection that might otherwise be skipped.
–
Greg DeanMay 26 '09 at 23:29

1

The point of the Dispose is not to clear up the memory of managed objects - that is the garbage collector's job. The point is to clear up unmanaged objects. There seems to be evidence that DataSets do not have any unmanaged references so theoretically don't need to have disposed called them. That being said, I've never been in a situation where I've had to go out of my way to call Dispose - I would just call it anyway.
–
cbpMay 26 '09 at 23:37

2

The primary use of IDisposable is to release unmanaged resources. Often times it also modifies state in a manner which makes sense for a disposed instance. (i.e. properties set to false, references set to null, etc.)
–
Greg DeanMay 26 '09 at 23:50

2

If there is a dispose method on an object it was put there for a reason regardless if it's for cleaning up unmanaged objects or not.
–
Chuck ConwayApr 10 '12 at 19:18